Method and apparatus for paging group handling

ABSTRACT

A method and apparatus for paging group handling includes grouping wireless transmit/receive units (WTRUs) into a paging group. The paging group is assigned a paging occasion, and an existence of a page is indicated to the WTRUs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/887,440, filed Jan. 31, 2007, which is incorporated by reference asif fully set forth.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

One of the efforts for the third generation partnership project (3GPP)long term evolution (LTE) program is to bring new technology, newarchitecture and new methods into the new LTE settings andconfigurations. The LTE program is undertaken in order to provideimproved spectral efficiency, reduced latency, and better utilization ofradio resources, thereby providing faster user experiences and richerapplications and services with less associated cost.

With regard to mobile terminal idle mode paging reception, the LTEsystem may use the downlink layer 1 (L1) and layer 2 (L2) controlsignaling channel to signal paging indicators to groups of wirelesstransmit/receive units (WTRUs) with the same paging group identity.However, this may not be practical in the implementation of certainaspects of paging group handling with respect to idle mode pagingfundamentals, (e.g., total system paging capacity, system paging loaddistribution, and flexibility in assigning WTRUs different discontinuousreception (DRX) cycle lengths within a single paging group of WTRUs).

It would therefore be beneficial to provide a method and apparatus forhandling paging groups.

SUMMARY

A method and apparatus for paging group handling is disclosed. Themethod includes grouping wireless transmit/receive units (WTRUs) into apaging group. The paging group is assigned a paging occasion, and anexistence of a page is indicated to the WTRUs.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1 shows an example wireless communication system including aplurality of WTRUs and a base station;

FIG. 2 is a functional block diagram of a WTRU and the base station ofFIG. 1;

FIG. 3 is a flow diagram of a method of paging group handling;

FIG. 4 shows an example base paging occasion;

FIG. 5 shows an example bitmap representation of paging groups; and

FIG. 6 is a diagram of an example LTE paging message.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to hereafter, the terminology “base station” includes but isnot limited to a Node-B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment.

FIG. 1 shows a wireless communication system 100 including a pluralityof WTRUs 110 and a base station 120. As shown in FIG. 1, the WTRUs 110are separated, for purposes of example, into three paging groupsdesignated “A” which includes WTRUs 110 ₁, “B” which includes WTRUs 110₂, and “C” which includes WTRUs 110 ₃. The WTRUs 110 are incommunication with the base station 120. It should be noted that,although an example configuration of WTRUs 110 and base station 120 isdepicted in FIG. 1, any combination of wireless and wired devices may beincluded in the wireless communication system 100.

FIG. 2 is a functional block diagram 200 of a WTRU 110 and the basestation 120 of the wireless communication system 100 of FIG. 1. As shownin FIG. 2, the WTRU 110 is in communication with the base station 120and both are configured to perform a method of paging group handling.

In addition to the components that may be found in a typical WTRU, theWTRU 110 includes a processor 115, a receiver 116, a transmitter 117,and an antenna 118. The processor 115 is configured to perform a paginggroup handling procedure. The receiver 116 and the transmitter 117 arein communication with the processor 115. The antenna 118 is incommunication with both the receiver 116 and the transmitter 117 tofacilitate the transmission and reception of wireless data.

In addition to the components that may be found in a typical basestation, the base station 120 includes a processor 125, a receiver 126,a transmitter 127, and an antenna 128. The processor 125 is configuredto perform a paging group handling procedure. The receiver 126 and thetransmitter 127 are in communication with the processor 125. The antenna128 is in communication with both the receiver 126 and the transmitter127 to facilitate the transmission and reception of wireless data.

The arrival of an incoming page at a WTRU 110 is a random event. Thisshould be considered in light of the requirements to maintain the WTRU110 in idle mode as long a practicable for power savings. The WTRU 110should “wake up” regularly to check the arrival of a page. It may bedesirable, therefore, to address a suitable amount of paging groups ofWTRUs 110, while allowing different WTRUs 110 within a paging group tohave different DRX cycle lengths. In one example, a minimum pagingoccasion time unit is an LTE frame.

Accordingly, FIG. 3 is a flow diagram of a method 300 of paging grouphandling. In step 310, WTRUs 110 are grouped into paging groups. Forexample, referring back to FIG. 1, WTRUs 110 ₁ are placed in paginggroup A, WTRUs 110 ₂ are placed in paging group B, and WTRUs 110 ₃ areplaced in paging group C.

In an LTE network, a paging group having a paging group identity (PG-ID)may be defined in a number of ways. For example, WTRUs can be groupednumerically by the WTRU entity, such as the international mobilesubscriber identity (IMSI), or the temporary mobile subscriber identity(TMSI). Due to the temporary nature of the TMSI, however, the IMSI maybe a more stable identity to be used in LTE for paging handling in idlemode. Alternatively, the paging group can be grouped logically by thenetwork operators for the purpose of service classification ordistinction, network service treatment differential and paying customerprioritization.

Where the grouping is numerical, the following example methods may beutilized: PG-ID=(IMSI mod DRX-cycle-len(gth)), or PG-ID=(IMSI divDRX-cycle-len)+(IMSI mod DRX-cycle-len). The resulting paging group,PG-ID, becomes the basic-paging-occasion-offset frame number when allthe paging occasions for a particular WTRU are determined and a group ofWTRUs with a similar numerical property of their IMSIs (or TMSI) withrespect to the shortest DRX cycle length is defined by the LTE system. AWTRU 110 can derive its own PG-ID by the IMSI it is assigned to with oneof the above equations. For example, For example if the a WTRU 110 isassigned an IMSI of 18922, and the DRX-cycle-len from the network,(e.g., published in a system information broadcast), is 32, then thePG-ID for that WTRU would be ten “10” in accordance with the firstequation, (i.e., 18922 mod 32=10).

Where the grouping is logical, network operators may want to group theWTRUs 110 into sets of WTRUs based upon certain priorities or those thatrequire differential treatment. In this case, WTRUs 110 are assigned todifferent logical paging groups by the service/network provider within aparticular service category, within a network origin, or using otherproperties. Example groupings may depend on the WTRU IMSI's mobilenetwork code (MNC), mobile country code (MCC), or on certain attributesof the WTRU's IMSI's mobile station identification number (MSIN). Thenetwork operators may use some of the following possible combinations todefine the paging occasion group identity:

PG-ID=eUTRAN-Prefix∥MNC∥eUTRAN-suffix;

PG-ID=eUTRAN-Prefix∥MCC∥eUTRAN-suffix; or

PG-ID=eUTRAN-Prefix∥(MSIN logical-partition)∥eUTRAN-suffix,

where the eUTRAN-Prefix and eUTRAN-suffix can be any value, except onethat is used for another PG-ID in subsequent operations. Alternatively,a PG-ID with other desired properties may be assigned.

Since idle mode WTRUs wake up periodically to check if the E-UTRANnetwork has sent, or is sending a particular paging indication to it andto its group of WTRUs, paging occasions are assigned to the paginggroups (step 320). A paging occasion, which may occur at the beginningof an LTE frame, defines a particular time that a WTRU should wake up tocheck if it is being paged. The LTE system distributes these pagingoccasions in the time domain so that the paging load at any time isequalized, and the paged WTRU receives the paging with minimum delaywith respect to its sleep/wake-up cycle, (i.e., DRX cycle).

In step 330, WTRUs within a paging group may be assigned different DRXcycle lengths. Accordingly, for a particular paging group, with respectto the PG-ID, the system will have to determine abase-paging-occasion-offset that would be equivalent to a frame number.The subsequent and continuous paging occasions are built on top of thebase-paging-occasion-offset. This base-paging-occasion-offset may bereferred to as the PO-GP.

In the total paging occasion distribution for different WTRUs havingdifferent DRX cycle lengths, the PO-GP indicates, at the beginning ofthe system frame, a number scale that is used as the offset framenumber. This may be the shortest DRX cycle length by the LTE system dueto the variable DRX cycle length assignment that a WTRU may have,regardless of the paging group in which it belongs. A particular WTRU110 may have the shortest or longest DRX cycle. FIG. 4 shows an examplebase paging occasion 400. FIG. 4 shows a group of WTRUs 110 within thePG-ID “A” that also include the PO-GP of “1”. These WTRUs have differentDRX-Cycle-lengths which are shown as 8 or 16. Accordingly, the WTRUs mayexpect their respective paging occasions in the time scale of systemframe numbers (SFNs). For example, a WTRU with DRX-cycle-len=8 wouldexpect its paging at SFN 1, 9, 17, 25, 33, and the like, while a WTRUwith DRX-cycle-len=16 may expect its paging at 1, 17, 33, and the like.A choice between DRX-cycle-lengths may include considerations ofperformance versus power savings. For example, the WTRU with a DRX cyclelength of 8 may consume more power, but it may have more chances toreceive paging, resulting in faster incoming call reception, and thelike.

Similarly to the PG-ID, the PO-PG may be determined numerically orlogically. For example, the PO-PG may be determined numerically inaccordance with the equation: PO-GP=PG-ID mod DRX-Cycle-Len, where theDRX-cycle-len is the minimum DRX cycle length defined by the system.

The PG-OP can also be organized logically, especially for those paginggroups formed logically. In this case, the PG-ID is converted to PO-GPvia a mapping table if there is no short formula to numericallytranslate from PG-ID to PO-GP where, for instance, the PG-IDs are notconsecutively sequenced. The mapping table may also be used to achievethe intended PO-GP distribution, or to retain the flexibility ofassignment, so that, for example, reassignment can be arranged easily.Table 1 below shows an example mapping table of a PG-ID to a PO-GP.

TABLE 1 PG-ID PO-GP (Allocated WTRU (Base Paging Occasion offsetGroup-Id) Group) PG-ID A 0 PG-ID B 1 PG-ID C 2 PG-ID D 2 PG-ID E 3 ; ; ;; ; ; PG-ID N_(max-PG-ID) φ

It should be noted that N_(max-PG-ID) is the maximum number of paginggroups the LTE system will be able to accommodate. The φ is an absolutevalue smaller or equal to the shortest DRX-cycle-len minus one(φ<shortest-DRX-cycle-len−1). Multiple paging groups can be assigned tothe same PO-GP.

From a system perspective, the PO-GP needs to be distributed to all theframe occasions covered in the shortest DRX cycle, so as to even thepaging load as well as to maintain the paging performance. Additionally,more than one paging group can be assigned to the same PO-GP so that DRXcycle length flexibility can be maintained and system paging capabilitymay be maximized.

In an LTE WTRU and system, the overall continuous paging occasions,(i.e., paging occasion frame numbers “PO-FN”) with any DRX cycle lengthsare calculated by PO-FN=PO-GP+n*DRX-cycle-len, where n=0, 1, 2, . . . ,such that the resulting PO-FN does not exceed the maximum system framenumber limit and the DRX-cycle-len is assigned per WTRU. In this manner,the paging status for any particular WTRU 110 is indicated (step 340).

At each paging occasion, PO-FN, a WTRU 110 in idle mode DRX cycle, aswell as WTRUs 110 in its paging occasion group or other groups with thesame PO-GP, wake up to read the paging indication (step 350) based onthe PO-GP it is in and DRX cycle length it is assigned to. Since morethan one group of WTRUs 110 may be in the process of checking the pagingindicator to find the paging status toward its group at the same time,the system may need to accommodate more paging groups in the limitedspace of the paging indicator, and, at the same time, efficientlyorganize the space for multiple paging group status indication.

One way to accommodate the requirements is to use a bitmap method forindicating the paging status of the paging-groups belonging to apaging-occasion (PO-GP). A bit in the map, or paging status bit, wouldindicate whether a particular paging group is either being paged, (e.g.,bit value “1”) or not paged, (e.g., bit value “0”). FIG. 5 shows anexample bitmap representation of paging groups 500. As shown in FIG. 5,paging group ID “A” includes a PO-GP of 1, paging group ID “B” includesa PO-GP of 4, and paging group ID “C” includes a PO-GP of 1. Each WTRUwithin a paging group reads the paging status bit in the bitmap duringthe group's paging occasion and in accordance with the WTRU'sDRX-cycle-len, as indicated by the arrows shown in FIG. 5, in order todetermine whether or not a page exists for the WTRU.

The bitmap construction essentially is a line of up of N bits with bit-0representing the paging group with the smallest PG-ID, bit-1representing the group with the next value of PG-ID, and so on. Table 2,below shows an example bitmap for one PO-GP.

TABLE 2 Bit-0 Bit-1 Bit-2 ; ; ; Bit-n PG-ID-a1 PG-ID- PD-ID- ; ; ; ;PG-ID- a2 a3 anwhere G-ID-a1<PG-ID-a2<PD-ID-a3< . . . <PG-ID-an.

There will be N, (i.e., N=shortest DRX cycle length−1), bitmaps in thesystem, with one for each PO-GP position. The E-UTRAN system broadcaststhis PG-ID/PO-GP mapping in the system information broadcast. Table 3,below, shows a PG-ID mapping bitmap per paging occasion.

TABLE 3 PO-GP 0 PO-GP 1 PO-GP 2 ; ; ; PO-GP N Bit-0 PG-ID a PG-ID PG-IDPG-ID x1 y1 z1 Bit-1 PG-ID b PG-ID PG-ID PG-ID x2 y2 z2 ; ; ; ; ; ;Bit-K PG-ID S PG-ID PG-ID ; ; ; xn yn

However, if the E-UTRAN system has adopted the approach described inTable 1, above, and published Table 1, then the WTRU 110 may calculatethe bit position of its paging group based on the rule specified inTable 2 above.

As described previously, a WTRU 110 in idle mode wakes up at the pagingoccasions indicated by the PO-FN and checks on the paging indicator.Based on its assigned PG-ID and the bit position in the bitmap, the WTRU110 checks whether its paging group, or groups, has an active page,which may include whether the bit position J in the paging-group-bitmapis set or not.

If the bit position is set, (i.e., a page is indicated), the WTRU 110reads the LTE physical channel (PDSCH) (step 360), described by theradio bearer (RB)-allocation portion of the paging indicator, where ahigher layer paging message will list the exact IMSI/TMSI of each of theWTRUs 110 being paged. If the WTRU 110 finds an exact match of itsIMSI/TMSI, it indicates that a page exists for the WTRU 110.

Additionally, the bitmap is defined by the E-UTRAN and is broadcast foreach of the PO-GPs in the system information when the PO-GP is givensuch information with respect to PG-IDs. Only one bitmap for each PO-GPneeds to be broadcast. Accordingly, while the WTRUs in any particulargroup may have varying DRX-cycles, they are able to use the same bitmapfor all PG-FNs.

In one example, an LTE Paging message may be used when a WTRU getssignaled for a definite page, and where the exact WTRU is directlyaddressed to reinstate the paging. FIG. 6 is an example diagram of anexample LTE paging message 600.

As shown in FIG. 6, a WTRU at frame 9 receives a paging indicator(hatched), which contains a “Paging Status Bitmap” and an “RB (LTEresource block) allocation information” for the WTRU to receive the realpaging message, (e.g., the LTE paging message), from another channelthat carries the real paging message. This gives the timing and physicalchannel information. If the bitmap status bit for its paging-group isnot set, then the WTRU may not read the real paging message in order toconserve power.

The LTE paging message 600 contains the paging records, (i.e., the realWTRU IMSIs), for each really paged WTRUs. A WTRU checks the bitmap tosee its PG-ID bit is set and uses the RB allocation information to readthe LTE paging message 600. A WTRU ascertains that it is paged when ithas confirmed that its IMSI is in the paging records.

The number of IMSIs capable of being addressed in an LTE paging messagerepresents the LTE paging capacity at its maximum, and should bedesigned to take peak paging load into consideration. If the definedIMSI carrying capability is not big enough, then certain WTRUs 110 maybe left out of the paging confirmation and may not receive incomingcalls in time.

In addition, the LTE paging message paging record should contain as manypaged WTRU IMSIs as possible. If allocated RB space is limited,extensions can be made to include all the paging records/IMSIs. Theextension could be made in the paging indicator RB-allocation part,where a pointer can indicate another, or auxiliary RB-allocation for theLTE paging message extension. Alternatively, the extended space may beresolved in the PCH domain, where extra space can be temporarilyprovided for the LTE Paging message extension.

Also, to accommodate the many IMSIs in the message as possible,signaling compression can be applied. The duplicated MCCs and MNCs donot need to be included in the message, resulting in direct list ofMSINs of IMSIs in most instances, thus saving message space. Theformatting of the IMSI may start with the MCC, and then move to the MNC,and lastly the MSIN. The MCC is the leading index, then the MNC. If thenext MCC or MNC is not different than the previous one, then they do notneed to be included. A WTRU search for an IMSI match can also takeadvantage of this formatting rule, skipping unmatched MCCs and MNCs bydirectly going to the matching MCC and MNC to increase matching processefficiency.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB)module.

1. A method for discontinuous reception (DRX) of paging from idle modein a long term evolution (LTE) user equipment (UE), the methodcomprising: deriving a first value from a second value modulo a thirdvalue, wherein the second value is derived from an international mobilesubscriber identification (IMSI) of the UE and the third value isderived from a DRX cycle of the UE; deriving a fourth value fromdividing a fifth value by the third value; deriving paging frames basedon the first value and the fourth value; and in idle mode, monitoring,by the LTE UE, for pages in the derived paging frames and being in DRXin frames other than the derived paging frames.
 2. The method of claim 1wherein the DRX cycle of the UE is different than the DRX cycle of otherUEs.
 3. A long term evolution (LTE) user equipment (UE) comprising: aprocessor, operatively coupled to a transmitter and a receiver, whereinthe processor is configured to derive a first value from a second valuemodulo a third value, wherein the second value is derived from aninternational mobile subscriber identification (IMSI) of the UE and thethird value is derived from a discontinuous reception (DRX) cycle of theUE; the processor is further configured to derive a fourth value fromdividing a fifth value by the third value; the processor is furtherconfigured to derive paging frames based on the first value and thefourth value; and in idle mode, the processor and receiver areconfigured to monitor for pages in the derived paging frame and being inDRX in frames other than the derived paging frames.
 4. The LTE UE ofclaim 3 wherein the DRX cycle of the UE is different than the DRX cycleof other UEs.
 5. A wireless long term evolution (LTE) network devicecomprising: a processor configured to derive a first value from a secondvalue modulo a third value, wherein the second value is derived from aninternational mobile subscriber identification (IMSI) of a userequipment (UE) and the third value is derived from a discontinuousreception (DRX) cycle of the UE; the processor is further configured toderive a fourth value from dividing a fifth value by the third value;the processor is further configured to derive paging frames based on thefirst value and the fourth value; and the processor is furtherconfigured to page the UE in the derived paging frames on a conditionthat the UE is in an idle mode.
 6. The LTE network of claim 5 whereinthe DRX cycle of the UE is different than the DRX cycle of other UEs. 7.The LTE network of claim 5 wherein the wireless LTE network device is acomponent of a base station.